Route of Prostagland in F 2α Injection and Luteolysis in Mares 1

Abstract

Summary

Nine groups of pony mares (3/group) were used in a 3 × 3 factorial experiment. The factors were dose of PGF_2α (0, 0.25 or 1.25 mg) and route of administration (im, iu or il). Mares were lapa-rotomized and treated on day 7 postovulation. Jugular blood was collected for progesterone RIA at 0 (pretreatment) and 1, 6, 12, 24, 48 and 72 hr posttreatment.

In mares given either 0.25 mg or 1.25 mg PGF_2α, progesterone concentrations were not significantly different among the three routes at any of the posttreatment times studied except at 6 hr posttreatment. In mares given 0.25 mg, progesterone concentration at 6 hr was less (P < 0.05) for mares injected il than for mares injected im or iu. In mares given 1.25 mg, the concentration at 6 hr was less (P < 0.05) for mares injected im than for mares injected iu. Compared to pretreatment progesterone values, PGF_2α (0.25 mg and 1.25 mg groups combined) administration significantly decreased progesterone concentration by 12 hr posttreatment in mares injected im and by 24 hr in mares injected iu or il. In the iu group, a significant increase in progesterone concentration occurred between 1 and 6 hr followed by a significant decrease at 12 hr posttreatment.

There were no significant differences among the three routes for intervals from treatment to estrus or ovulation, length of posttreatment estrus or length of inter-ovulatory interval. Injection of either 0.25 mg or 1.25 mg PGF_2α significantly shortened the interval from treatment to estrus. Although 0.25 mg tended to shorten the interval from treatment to ovulation and inter-ovulatory interval, these two end points were significantly shortened only in mares given 1.25 mg PGF_2α.

Results indicated that local administration (iu or il) did not improve the luteolytic efficacy of PGF_2α over systemic administration (im).